Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $197.99   11.644%   $221.044   $221.04   $221.05   $221.00  
  Purchase #2 $110.33   11.252%   $122.7443   $122.74   $122.75   $122.70  
  Purchase #3 $178.46   8.695%   $193.9771   $193.98   $194.00   $194.00  
  Purchase #4 $108.49   11.663%   $121.1432   $121.14   $121.15   $121.10  
  Purchase #5 $94.44   7.188%   $101.2283   $101.23   $101.25   $101.20  
  Purchase #6 $101.35   7.279%   $108.7273   $108.73   $108.75   $108.70  
  Purchase #7 $124.29   5.641%   $131.3012   $131.30   $131.30   $131.30  
  7 purchase totals = $915.35       $1,000.1654   $1,000.16   $1,000.25   $1,000.00